0.75 X 200x =0.8 X 200(x-1)0.75 x =0.8(x-1)0.75x=0.8x-0.80.8x-0.75x=0.80.05x=0.85x=80x=16
150x=0.8X200x-200150x/200x=0.8-2000.75x=199.2x=265.6
简单